WORCESTER — Attorney General Martha Coakley is supporting a gay couple's legal battle against the Diocese of Worcester after the pair was allegedly denied the right to buy a church-owned mansion in Northbridge.

Two Sutton men, James E. Fairbanks and Alain J. Beret, a married gay couple, filed a civil suit in Worcester Superior Court in 2012 against the diocese and its real estate agent after their offer to buy the Oakhurst Conference and Retreat Center, a 44-bedroom mansion in the Whitinsville section of Northbridge, was rejected by the Diocese of Worcester.

The lawsuit contends the diocese ended the deal because the men are gay and might hold same-sex weddings on the property.

"In this case, we believe that this family was unfairly discriminated against by the Diocese when it refused to sell them property based on their sexual orientation," Ms. Coakley said in a written statement.

The diocese has denied the allegations.

In court filings, church officials have argued state anti-discrimination laws do not apply to their conduct and cite legal exemptions and other constitutionally protected rights. Ms. Coakley contends the state's anti-discrimination law includes the sale of public and commercial property owned by the diocese.

An April 22 hearing has been scheduled.

The brief contends that the diocese's religious rights are not burdened by the sale of the property to Mr. Fairbanks and Mr. Beret. In addition, the attorney general contends that Massachusetts' interest in eliminating discrimination on the basis of sexual orientation outweighs any burden on religious rights imposed by applying the anti-discrimination statute in this case.

Mr. Fairbanks and Mr. Beret had plans to renovate the aging mansion and turn it into a banquet facility. The mansion would be used to host weddings and other events and be their personal residence. Owned by House of Affirmation Inc., an affiliate of the diocese, the site at 120 Hill St. in Whitinsville was formerly known as the House of Affirmation, a treatment center for pedophile priests that closed in the 1980s.

The prospective buyers have been in a relationship for more than 30 years and married since 2004. They made an offer for the property in May 2012.

In their lawsuit, the couple said that in June 2012, a day after they made a revised $550,000 offer for Oakhurst and six acres of the 26-acre site, Monsignor Thomas Sullivan sent the following email to the diocesan broker:

"I just went down the hall and discussed it with the bishop. Because of the potentiality of gay marriages there, something you shared with us yesterday, we are not interested in going forward with these buyers. I think they're shaky anyway.

"So, just tell them that we will not accept their revised plan and the Diocese is making new plans for the property. You find the language."

The email was later inadvertently forwarded to Mr. Beret, according to the suit. The couple is seeking unspecified monetary damages for alleged violations of state housing discrimination laws and infliction of emotional distress.

Monsignor Sullivan, who oversees the sale of diocesan property, is named as a defendant in the suit, along with the House of Affirmation Inc., Bishop Robert McManus and Eastern Alliance Realty, LLC, which acted as an agent for the diocese in the negotiations.

After the lawsuit was filed in September, the lawyer for the diocese in this matter stated that no one ever asked or knew the couple's sexual orientation.

"From the diocese point of view, this case is not about discrimination against gay persons. It's simply a failed real estate transaction," James G. Reardon Jr. said in September. "The buyers never came up with sufficient financing. They never signed a purchase and sale agreement. They tried to rework the negotiations for the property, so the deal never went through."

Mr. Reardon could not be immediately reached for comment Thursday.

Ms. Coakley has included decisions by the courts, laws passed by legislators, orders from the governor and enforcement actions by her office to support her argument.

"Our laws provide important protections for religious organizations and people of faith," said Ms. Coakley, who is a Democratic candidate for governor this year. "These laws also strike a balance between religious freedoms and the rights of individuals to be free from discrimination."

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